The present invention relates to a body fat measuring device for measuring the amount of fat in a human body.
The body composition of a human body is made up of muscles, bones, fat and others. The value of impedance of a human body containing a large amount of fat components differs from that of a human body containing a large amount of muscle components. More specifically, bio-impedance has such a nature that as fat components increase, the value of impedance increases and as components containing water increase, the value of impedance drops. When obtaining the amount of fat contained in the body composition by utilizing this nature, the following method is usually taken: Electrodes are attached to dermal surfaces at distal sites of the body such as the tips of fingers of right and left hands, the tiptoes of right and left feet, and the soles of right and left feet. An alternate current or voltage having a frequency of about several tens of KHz to 100 KHz is applied to these electrodes to measure the impedance of the body composition present between the distal sites. Then, the amount of body fat is calculated from the value of impedance thus obtained and personal data such as age, sex and height.
In recent years, the amount of fat contained in the body composition has been considered to be an index for health care and attracted the attention of ordinary people a great deal. Accordingly, demands toward body fat measuring devices for family or personal use have been increasingly growing. With such a background, there have been developed and sold a variety of inexpensive body fat measuring devices capable of measuring the amount of body fat with easy operation.
Known body fat measuring devices generally employ the measuring method called xe2x80x9cthe two terminal methodxe2x80x9d (the two electrode method) or the measuring method called xe2x80x9cthe four terminal methodxe2x80x9d (the four electrode method), and measure the amount of body fat in the body composition by measuring, in an easy way, body inter-distal-site impedance (i.e., the impedance between discrete distal sites of the body to which electrodes are attached) or body composition impedance that excludes the composition of the body at the distal sites.
FIG. 9(a) is a measurement principle diagram illustrating the principal of measurement of body composition impedance by a body fat measuring device which utilizes the conventional two terminal method and FIG. 9(b) is a circuit diagram for explaining the measurement principle. This body fat measuring device 100 comprises two electrodes 101a, 101b on its top surface. The two electrodes 101a, 101b are connected to a constant current circuit 102 and a patient steps on the measuring device 100 with one foot placed on the electrode 101a and the other foot on the electrode 101b, so that a constant current Ic is supplied to the human subject from the constant current circuit 102. The constant current circuit 102 is comprised of (i) an operational amplifier 103 for outputting the constant current Ic and (ii) a reference resistor 104 having a given value Rs for controlling the circuit so as to allow the operational amplifier 103 to output the constant current Ic. The electrodes 101a, 101b are connected to a voltage measurement circuit 105 and a voltage V generated between the electrodes 101a, 101b in a condition in which the constant current Ic is applied thereto is measured by the voltage measurement circuit 105. The voltage measurement circuit 105 comprises (i) an operational amplifier 106 for outputting the voltage V generated between the electrodes 101a, 101b in response to a voltage signal released from the electrodes 101a, 101b; (ii) input resistors 107a, 107b for the operational amplifier 106; and (iii) a resistor 108 for a negative feedback circuit.
In the thus-arranged body fat measuring device 100, where the body inter-distal-site impedance is Zo, the contact impedance between the electrode 101a and the dermal surface of a foot of the human subject is RX1, the contact impedance between the electrode 101b and the dermal surface of another foot is RY1, the relationship represented by the following equation exists between the impedances Zo, RX1, RY1, the constant current Ic, and the voltage V.
(RX1+Zo+RY1)xc2x7Ic=V
That is,
Zo+RX1+RY2=V/Ic
Herein, if the sum of the contact impedances RX1, RY1 (RX1+RY1) is much smaller than the body inter-distal-site impedance Zo, in other words, if Zo+RX1+RY2≈Zo, the body inter-distal-site impedance Zo can be obtained.
By performing calculation based on the body inter-distal-site impedance Zo thus obtained and personal data such as the age, sex and height of the patient which have been input to the body fat measuring device 100 beforehand, the amount of body fat can be obtained. It should be noted that the body inter-distal-site impedance Zo is obtained by combining body distal site surrounding composition impedance to body composition impedance.
Next, a body fat measuring device using the conventional four terminal method will be explained. FIG. 10(a) is a diagram showing the measurement principal of a body composition impedance in a body fat measuring device which utilizes the conventional four terminal method and FIG. 10(a) is a circuit diagram for explaining the measurement principle. The body fat measuring device 110 comprises four electrodes 111a, 111b, 112a and 112b on the top surface thereof. A patient steps on the measuring device 110 with one foot placed on the electrodes 111a, 112a and the other foot on the electrodes 111b, 112b. The electrodes 111a, 111b are connected to a constant current circuit 113, and when the patient puts one foot on the electrode 111a and the other on the electrode 111b, a current Id is supplied to the human subject from the constant current circuit 113.
The electrodes 112a, 112b are connected to a voltage measurement circuit 114 and a voltage generated between the electrodes 112a, 112b when the constant current Id is applied thereto is measured. Herein, the constant current circuit 113 is comprised of (i) an operational amplifier 115 for outputting the constant current Id and (ii) a reference resistor 116 having a given value Rs for controlling the circuit so as to allow the operational amplifier 115 to output the constant current Id. The voltage measurement circuit 114 is comprised of (i) an operational amplifier 117 for outputting the voltage V generated between the electrodes 112a, 112b in response to a voltage signal released from the electrodes 112a, 112b; (ii) input resistors 118a, 118b for the operational amplifier 117; and (iii) a resistor 119 for a negative feedback circuit.
In the thus-arranged body fat measuring device 110, where the body composition impedance to be measured is Zi, the contact impedances between the electrodes 111a, 111b, 112a, 112b and the dermal surfaces of the feet of the human subject are RX1, RY1, RX2 and RY2, respectively, the resistance values of the input resistors 118, 118b of the operational amplifier 117 are set to be sufficiently higher than the contact impedances RX2, RY2, whereby the constant current Id to be supplied between the electrodes 111a, 111b will not flow into the operational amplifier 117 and the amplification factor of the operational amplifier 117 will not be affected even if the contact impedances RX2, RY2 fluctuate. Accordingly, a voltage generated between virtual intersections P and Q in the body, that is, the voltage V generated at both ends of the body composition impedance Zi excluding the contact impedances and body distal site surrounding composition impedances can be measured by the voltage measurement circuit 114. Zi is calculated from the equation Zi=V/Id based on the voltage V thus obtained and the constant current value Id, thereby obtaining the body composition impedance Zi that is not affected by the contact impedances and the body distal site surrounding composition impedances. Regarding the body distal site surrounding composition impedances, since articulates have great impedance values irrespective of the amount of body fat, it is necessary to measure impedance which excludes the impedances of the compositions surrounding body""s distal sites particularly in cases where the composition to be measured includes articulates.
The amount of fat in the body of the patient can be obtained by calculation based on the body composition impedance Zi thus obtained and personal data such as the age, sex, height etc. of the patient which have been input to the body fat measuring device 110 beforehand.
As prior art techniques associated with the present invention, there are proposed body fat measuring devices in Japanese Patent Publication (KOKAI) Gazette No. 7-79938 (1995) and Published Japanese Translations of PCT International Publication for Patent Applications No. 10-510455 (1998), according to which the impedance of an internal organ in a body is measured by the above-described four terminal method to be utilized in measuring the amount of fat. FIG. 11 diagrammatically shows the principle of the measurement of an internal organ composition impedance Zj in the above prior art body fat measuring devices.
In a body fat measuring device 120 associated with the above prior art, there are provided eight electrodes E1, E2, E3, E4, E5, E6, E7, and E8 which are paired and attached to the right-left pairs of sites on the hands and foot of a human subject, respectively. One group of the electrodes E1, E3, E5, E7 is connected to a constant current circuit, whereas the other group of the electrodes E2, E4, E6, E8 is connected to a voltage measurement circuit. It should be noted that these constant current circuit and voltage measurement circuit have the same configuration as those of the above-described body fat measuring devices 100, 110 which utilize the two terminal method and the four terminal method, respectively. In the thus-arranged body fat measuring device 120, a current is applied between the electrodes E1 and E3 and the voltage between the electrodes E2 and E4 is measured, thereby obtaining the value of {circle around (1)} Z1+Z2. Similarly, a current is applied between the electrodes E5 and E7 and the voltage between the electrodes E6 and E8 is measured, thereby to obtain the value of {circle around (2)} Z4+Z5; a current is applied between the electrodes E1 and E5 and the voltage between the electrodes E2 and E6 is measured, thereby obtaining the value of {circle around (3)} Z1+Zj+Z4; and a current is applied between the electrodes E3 and E7 and the voltage between the electrodes E4 and E8 is measured, thereby obtaining the value of {circle around (4)} Z2+Zj+Z5. Based on the results of these measurements, the internal organ composition impedance Zj is calculated from the equation {{circle around (3)}+{circle around (4)}xe2x88x92({circle around (1)}+{circle around (2)})}/2. Then, the amount of body fat is calculated from the internal organ composition impedance Zj.
Japanese Patent Publication (KOKAI) Gazette No. 5-49050 (1993) discloses a body fat measuring device in which body inter-distal-site impedance which is composed of body composition impedance and body distal site surrounding composition impedance is measured, and the amount of body fat is calculated based on the measured impedance and the personal data on the patient.
Since the body fat measuring device 110 shown in FIG. 10 and utilizing the four terminal method is designed to measure a voltage generated in the body composition that excludes the composition surrounding body distal sites from the contact impedance between the feet of the human subject and from the all the impedances present between the distal sites of the body, the measuring device 110 requires the operational amplifier 117 which constitutes the voltage measurement circuit 113, the input resistors 118a, 118b for the operational amplifier 117, and the resistor 119 for the feedback circuit. As a result, the configuration of the measuring device becomes large in scale, and the number of wires and circuits increases, inevitably leading to increased cost.
The prior art body fat measuring device 110 utilizing the four terminal method needs a pair of electrodes (two electrodes) for each measuring point (four electrodes in total) in order to measure the body composition impedance Zi from two sites of the body. In addition, wires and various circuits are connected to each electrode so that a large system configuration is involved, resulting in increased cost.
The prior art body fat measuring device 100 shown in FIG. 9 and employing the two terminal method has another problem. This device 100 is designed to obtain the body inter-distal-site impedance Zo including the contact impedances RX1, RY1 upon condition that the sum of the contact impedances RX1, RY1 is sufficiently smaller than the body inter-distal-site impedance Zo. Since a different amount of water and other deposits are present on the dermal surface of a body in each occasion, the values of the contact impedances RX1, RY1 vary more or less so that it becomes difficult to correctly, stably obtain the body inter-distal-site impedance Zo. Additionally, the body inter-distal-site impedance Zo includes the impedance of the composition surrounding body distal sites and, therefore, the impedance Zo sometimes has a great impedance value irrespective of the amount of fat within the body of the patient. As a result, the body fat measuring device 100 fails in correctly measuring the amount of body fat.
The body fat measuring device 120 for measuring the internal organ composition impedance Zj shown in FIG. 11 also suffers from problems: Since it needs eight electrodes in total (two electrodes for each hand and each foot), many wires and circuits become necessary which leads to a large system configuration and increased cost. In addition, when measuring the impedance of the cross section of the trunk of a body, many pairs of electrodes are attached with the trunk between each pair, and a voltage is measured between each opposed pair of electrodes. In this case, a pair of electrodes is necessary for each measuring point so that a large number of electrodes are involved, resulting in increases in the number of wires and circuits and in cost.
The body fat measuring device disclosed in Japanese Patent Publication (KOKOKU) Gazette No. 5-49050 measures the body inter-distal-site impedance that includes the body distal site surrounding composition impedance having a large value irrespective of the amount of body fat and obtains the amount of body fat based on the measured body inter-distal-site impedance. Therefore, this measuring device also has difficulty in correctly measuring the amount of body fat.
The present invention is directed to overcoming the above-described problems and a prime object of the invention is therefore to provide a body fat measuring device capable of accurately measuring body composition impedance which excludes contact impedance generated between each electrode and the dermal surface of a human object and body distal site composition impedance so that the amount of fat within the body of the human subject can be measured with high accuracy.
In accomplishing the above prime object, there has been provided, in accordance with the invention, a body fat measuring device for measuring the amount of body fat within a body, the device comprising:
(a) a single or a plurality of electrodes in contact with each of a plurality of sites on the dermal surface of the body;
(b) a power supply circuit for applying a constant current or voltage to the electrodes;
(c) impedance measuring means for switching the electrodes to be connected to the power supply circuit such that a contact impedance and a body distal site surrounding composition impedance are present between the electrodes or such that a contact impedance, a body distal site surrounding composition impedance and a body composition impedance are present between the electrodes, whereby the value of the composite of the contact impedance and the body distal site surrounding composition impedance and the value of the composite of the contact impedance, the body distal site surrounding composition impedance and the body composition impedance are respectively measured; and
(d) calculating means for calculating the value of the body composition impedance based on the measured values obtained by the impedance measuring means.
In the invention, one or a plurality of electrodes are disposed so as to contact each of a plurality of sites on the dermal surface of a body. The impedance measuring means measures the value of the composite of a contact impedance and a body distal site surrounding composition impedance and the value of the composite of a contact impedance, a body distal site surrounding composition impedance, and a body composition impedance. The calculating means then calculates only the value of the body composition impedance, based on the measured values. Personal data (age, sex, height, etc.) on a patient have been input beforehand, and the amount of body fat (body fat percentage) is calculated from the calculated value of the body composition impedance and the personal data, using a known method.
According to the invention, since the impedance measurement is made with different combinations of electrodes to which a current or voltage is applied, the influences of the contact impedances and the body distal site surrounding composition impedances are thoroughly eliminated by calculation so that a highly accurate body composition impedance value in which the amount of body fat of the patient is reflected and, consequently, a highly accurate body fat amount can be calculated. Since the need for electrodes for measuring a voltage generated within the body and a voltage measurement circuit can be obviated, the system construction can be simplified, leading to cost reduction.
The invention is preferably arranged as follows. The electrodes are provided such that a pair of electrodes are disposed so as to contact a first one of two dermal surface sites between which a body composition impedance to be measured is present and another pair of electrodes are disposed so as to contact a second one of the dermal surface sites. The electrodes in each pair are close to each other. The power supply circuit is connected to the pair of electrodes at the first site or at the second site by the impedance measuring means to measure the value of the composite of a contact impedance and a body distal site surrounding composition impedance, these impedances being present between the pair of electrodes to which the power supply circuit is connected. The power supply circuit is connected to one of the electrodes in the respective pairs at the first site and at the second site to measure the value of the composite of a contact impedance, a body distal site surrounding composition impedance and a body composition impedance, these impedances being present between the electrodes to which the power supply circuit is connected. The calculating means calculates the value of the body composition impedance based on the measured values.
With this arrangement, the influences of the contact impedances and the body distal site surrounding composition impedances can be thoroughly eliminated, similarly to the above case so that the value of the body composition impedance in which the amount of body fat of the patient is reflected can be calculated with high accuracy and the system configuration can be simplified, resulting in cost reduction.
The invention may be also arranged as follows. The electrodes are provided such that two electrodes are disposed so as to contact a first one of two dermal surface sites between which a body composition impedance to be measured is present and one electrode is disposed so as to contact a second one of the two sites. The two electrodes disposed at the first site are close to each other. The power supply circuit is connected to the two electrodes at the first site by the impedance measuring means to measure the value of the composite of a contact impedance and a body distal site surrounding composition impedance, these impedances being present between the electrodes to which the power supply circuit is connected. The power supply circuit is connected to one of the electrodes at the first site and the electrode at the second site to measure the value of the composite of a contact impedance, a body distal site surrounding composition impedance, and a body composition impedance, these impedances being present between the electrodes to which the power supply circuit is connected. Based on the measured values, the calculating means calculates the value of the body composition impedance.
With the above arrangement, the number of electrodes necessary for the device of the invention can be minimized, compared to the prior art body fat measuring device employing the four terminal method. In addition, the influences of the contact impedances and the body distal site surrounding composition impedances can be thoroughly eliminated to calculate the body composition impedance.
Another alternative of the invention is as follows. The electrodes are provided such that one electrode is disposed so as to contact each of the dermal surface sites which surround hands and feet respectively. The power supply circuit is connected by the impedance measuring means to the electrode in contact with one hand and to the electrode in contact with one foot to measure the value of the composite of a contact impedance, an arm composition impedance, a leg composition impedance and an internal organ impedance, these impedances being present between the electrodes to which the power supply circuit is connected. The power supply circuit is connected to the electrodes in contact with the hands to measure the value of the composite of a contact impedance and an arm composition impedance, these impedances being present between the electrodes to which the power supply circuit is connected. The power supply circuit is connected to the electrodes in contact with the feet to measure the value of the composite of a contact impedance and a leg composition impedance, these impedances being present between the electrodes to which the power supply circuit is connected. The calculating means calculates the value of the internal organ composition impedance, based on the measured values.
With the above arrangement, the measurement of the internal organ composition impedance which previously required eight electrodes can be made with four electrodes. This entails a reduction in the number of wires and circuits, resulting in simplification of the system configuration and cost reduction.
Preferably, the invention further comprises weight measuring means. With this arrangement, the value of weight, which is data necessary for the calculation of the amount of body fat from the body composition impedance, can be measured at the same time with the impedance measurement by the impedance measuring means. This leads to an improvement in the accuracy of the amount of body fat to be finally obtained.
It is also preferable to carry out the measurement of the impedances between the electrodes by the impedance measuring means while weight measurement is made by the weight measuring means, during a transient weight phenomenon state (weight fluctuation state). When the patient steps on the device with his dermal surface sites being brought into contact with the electrodes, the weight measuring means is in its fluctuated state, but a correct impedance measurement is possible. In the above arrangement, the wait time elapsing until the measuring device becomes ready for correct weight measurement is utilized for the impedance measurement so that the value of weight and the amount of body fat can be efficiently measured, while reducing the overall time required for the measurements.
In the invention, when the value of weight measured by the weight measuring means significantly fluctuates, being in an unstable condition, it is preferable to carry out the measurement of the impedances between the electrodes by the impedance measuring means while the weight measurement by the weight measuring means being made. With this arrangement, the impedances between the electrodes can be measured by the impedance measuring means during the wait time elapsing until the transient condition in which the value of weight to be measured by the weight measuring means fluctuates is settled. Therefore, even if a large number of cycles are required for the impedance measurement, in other words, even if it takes a long time to measure the impedances, the prolonged time will not affect the body fat amount measurement carried out simultaneously with the weight value measurement.
In the invention, when the value of weight measured by the weight measuring means does not fluctuate so much, being in a stable condition, it is preferable to interrupt the measurement of the impedances between the electrodes made by the impedance measuring means. Usually, the measurements of the values necessary for the calculation of the body composition impedance is completed by the time the value of weight becomes stable. When the value of weight has become stable, the measurement of the impedances between the electrodes is interrupted and the calculation of the body composition impedance is performed based on the measured values so that the amount of body fat can be output together with the value of weight. Accordingly, the measurement of the impedances between the electrodes can be carried out until the value of weight becomes stable and the calculation of the body composition impedance can be therefore performed with the latest measured values, so that the accuracy of the amount of body fat to be finally obtained can be increased.
In the invention, when the value of weight measured by the weight measuring means does not fluctuate so much, being in a stable condition, it is preferable to interrupt the measurement of the impedances between the electrodes made by the impedance measuring means while only the weight measurement being made. By thus performing the weight measurement continuously, it becomes possible to detect whether the value of weight is in a stable or unstable condition.